In some fields, it is useful to model objects in two or three dimensions. Modeling such objects proves useful in a variety of applications. For example, modeling the subsurface structure of a portion of the earth's crust is useful for finding oil deposits, locating fault lines and in other geological applications. Similarly, modeling human body parts is useful for medical training exercises, diagnoses, performing remote surgery or for other medical applications. The foregoing objects are exemplary only, and other fields may likewise find utility in modeling objects.
In the field of earth sciences, seismic sounding is used for exploring the subterranean geology of an earth formation. An underground explosion excites seismic waves, similar to low-frequency sound waves that travel below the surface of the earth and are detected by seismographs. The seismographs record the time of arrival of seismic waves, both direct and reflected. Knowing the time and place of the explosion, the time of travel of the waves through the interior can be calculated and used to measure the velocity of the waves in the interior. A similar technique can be used for offshore oil and gas exploration. In offshore exploration, a ship tows a sound source and underwater hydrophones. Low frequency, (e.g., 50 Hz) sound waves are generated by, for example, a pneumatic device that works like a balloon burst. The sounds bounce off rock layers below the sea floor and are picked up by the hydrophones. In either application, subsurface sedimentary structures that trap oil, such as faults and domes are mapped by the reflective waves.
In the medical field, a computerized axial topography (CAT) scanner or magnetic resonance imaging (MRI) device is used to collect information from inside some specific area of a person's body. Such modeling can be used to explore various attributes within an area of interest (for example, pressure or temperature).
The data is collected and processed to produce three-dimensional volume data sets. A three-dimensional volume data set, for example, may be made up of “voxels” or volume elements, whereby each voxel may be identified by the x, y, z coordinates of one of its eight corners or its center. Each voxel also represents a numeric data value (attribute) associated with some measured or calculated physical property at a particular location. Examples of geological seismic data values include amplitude, phase, frequency, and semblance. Different data values are stored in different three-dimensional volume data sets, wherein each three-dimensional volume data set represents a different data value.
Graphical displays allow for the visualization of vast amounts of data, such as three-dimensional volume data, in a graphical representation. However, displays of large quantities of data may create a cluttered image or an image in which a particular object or point of interest is partially obscured by undesirable data objects. There is therefore, a need to restrict the data displayed to a volume containing the object or point of interest.
One conventional solution requires the selective deletion of particular objects that are blocking the view of an object or point of interest or cluttering the display of the data. There are disadvantages associated with this solution, which include significant time consumption and the required deletion of an entire object instead of just that portion of the object that is outside the volume-of-interest. A more efficient and selective technique is needed, which will allow the selective removal of all undesirable objects, or portions thereof, outside the display of a particular volume-of-interest without having to individually select and remove each displayed object in its entirety.
Another approach is described in U.S. Pat. No. 6,765,570, which is assigned to Landmark Graphics Corporation and incorporated herein by reference (the “570 patent”). This patent describes a system and method for analyzing and imaging three-dimensional volume data sets using a three-dimensional sampling probe. The sampling probe can be created, shaped, and moved interactively by the user within a three-dimensional volume data set. As the sampling probe changes shape, size or location in response to user input, an image representing an intersection of the sampling probe and the three-dimensional volume data set is re-drawn at a rate sufficiently fast to be perceived in real-time by the user. In this manner, the user can achieve real-time interactivity by limiting the display of the three-dimensional volume data set to an image of an intersection of the sampling probe and the three-dimensional volume data set.
Although the '570 patent describes a method for limiting the display of a three-dimensional data set, the sampling probe is created in a default shape, size and location upon instantiation. As a result, the sampling probe must be manipulated to surround only an object or point of interest. The sampling probe, upon instantiation, may therefore, often include extraneous information or an image of only part of the object or point of interest. Manipulation of the probe shape, size and location to achieve a desired volume-of-interest containing the object or point of interest necessarily entails additional time consumption, which leads to inefficiency in producing a clear image of the object or point of interest. Further, the '570 patent fails to describe or disclose how to move an object or point of interest within the three-dimensional volume data set while it is surrounded by the sampling probe.
As such, there is a need for automatically imaging a volume-of-interest comprising an object or point of interest in a display of three-dimensional data, by reducing extraneous three-dimensional data in the display rather than adjusting the volume-of-interest. Further, there is a need for maintaining a volume-of-interest relative to the object or point of interest if the object or point of interest needs to be moved.